快猫短视频

PREHISTORIC Europe was covered by thick, closed-canopy forests, not open woods and grassland, according to an analysis of pollen records.

The findings undermine a controversial hypothesis that large herbivores such as the extinct aurochs limited tree growth. And they go to the heart of the question of how to conserve Europe鈥檚 鈥渘atural鈥� ecological state. Is it right, for example, to maintain highly biodiverse pastureland that may only exist because of agriculture?

For years, the conventional view was that after the last ice age 14,000 years ago, dense forest covered lowland Europe and only began to disappear with the encroachment of agriculture around 3000 years ago. One anomaly, however, was the large amount of pollen in peat bogs from ancient oak and hazels, which don鈥檛 do well in thick forests.

In 2000 Frans Vera, an ecologist at the Dutch ministry of agriculture in Driebergen, suggested herbivores grazing on saplings kept forests from encroaching on grassland (快猫短视频, 7 September 2002, p 35).

But when Fraser Mitchell of Trinity College, Dublin, Ireland, compared pollen samples from UK and Ireland, which did not have large herbivores, he found the profiles were similar. He also sampled pollen from hollows in modern closed-canopy forests. These always contained at least 60 per cent tree pollen, while open areas contained 50 per cent or less. All the British prehistoric hollows were 60 per cent or more tree pollen, suggesting closed-canopy forest (Journal of Ecology, vol 93, p 168). This presumably applied to continental Europe too.

Vera says the pollen observations are inconclusive. But Keith Kirby, a woodland ecologist with UK agency English Nature, in Peterborough, says that the new evidence is persuasive. 鈥淚t鈥檚 not a total killer blow. But I think it is a strong argument.鈥�